As fall descends on the United States every year, it happens: reports spread across news feeds that something scary is brewing in the Atlantic.
A reported tropical storm becomes a categorized hurricane making landfall, leaving us with flooding, destruction, and rising death rolls. The Facebook donate buttons proliferate, coastal friends are marking themselves "Safe," and inevitably in our current political climate, op-eds bemoaning the death sentence of climate change or denying its existence are shared on your timeline.
"Climate change" has become a buzzword and political bludgeon, but the fact is 70% of Americans believe it's happening, and 97% of climate scientists agree that it's caused by human activities. It's enough to embolden your friend's incessant need to tag his sweaty Instagram selfies with "#climatechange" for every day over 80 degrees in New York City.
That being said, is it possible to blame global warming as the reason behind Hurricane Florence being the second wettest storm behind Harvey? Or for Hurricane Michael's ranking as the third most powerful storm to ever hit the continental United States? There's also the question on everyone's mind—will we be seeing more destructive hurricanes every year?
The answers: Yes, yes, and it's complicated.
Category 4 Hurricane Michael makes landfall along the Florida panhandle.
Tropical cyclones, like hurricanes, are indeed affected by factors that climate change directly impacts like warmer air, warmer sea surface temperatures, and rising sea levels.
Warmer air contains more moisture than cooler air. Therefore, it makes sense that as the temperature of Earth's troposphere (the weather layer 5-10 miles above the ground) rises, the air can hold more water. This is happening across the globe. And when the air has more water… Yes, you guessed it: there's more rain. Average precipitation in the U.S. has been increasing, and heavier downpours are expected to increase across the country both in intensity and frequency (in the Northeast by a whopping 71%). This increased ability to hold onto moisture will affect hurricanes like Harvey and raise their ability to unleash massive loads of rain.
As for storm strength? Some scientific models project a 45-87% increase in the frequency of Category 4 and 5 hurricanes by 2100 if we continue along our rate of estimated global temperature increase. The warming of the ocean and higher sea levels are the main culprits here. By increasing the temperature of the sea surface, human activity can create hurricanes with 2-11% greater wind speeds that may deliver more damage when making landfall, and with sea levels expected to rise by 1-4 feet in the next 100 years, storm surges will only worsen intense coastal flooding. None of this is made better by reports that storms are slowing down, allowing them to inflict more damage for longer periods of time.
So, yes, the picture is bleak. But wait, there's more—what about the possibility of more storms in general, and more with greater ability to create massive damage? Take a breather, this is a nuanced question.
While there is evidence corroborating global warming causing wetter and stronger storms, the National Oceanic and Atmospheric Administration's research of storms over the past century and complex climate model projections for the future do not support the claim that climate change will lead to an increase in overall hurricane numbers in the Atlantic. In fact, there is some evidence that the number of hurricanes is actually decreasing.
Hurricane Harvey aftermathCNN
It also gets murky when trying to blame the global crisis on the dramatic increase of hurricane-related costs. The statistics are pretty sobering: three of the five costliest U.S. hurricanes on record occurred last year alone. 2017's Hurricane Harvey is tied for the top spot with Hurricane Katrina (2005) at $125 billion in damages, Hurricane Maria comes after them at $90 billion, and Hurricane Irma rounds out the list at $50 billion (Hurricane Sandy in 2012 is no. 4 at $65 billion).
From those numbers alone, it's easy to become despondent. However, a large reason for the heightened costs of natural disasters is an increase in development along U.S. coastal populations. Americans across the board, and probably your retired parents sick of Minnesotan winters, are flocking to the coasts, whose population grew by nearly 35 million people between 1970 and 2010. Coastal counties made up nearly 40% of the last U.S. census, and this is only estimated to increase. Where there are more people, there are more houses and businesses in harm's way when a hurricane descends on the area. Climate change notwithstanding, storm-related costs would only grow in these places.
I'll admit, it's a bit of a respite to be able to blame something other than global warming on one part of the gloomy picture that is our world's climate future. Climate scientists agree that it's not accurate or compelling to blame individual storms or other weather events on climate change. There are many factors that affect how a hurricane plays out, including planetary orbits, factors local to the creation and path of the storm, as well as year-to-year variances in global weather patterns. The 1900s saw many terrible storms, including the deadliest in our history (by far) at the turn of the century.
However, when looking at overall trends around the world, the case is clear: climate change is happening and it's not going away. It's likely to make hurricanes more severe, unleashing more powerful wind, rain, and flooding.
Perhaps it's best to quote Michael Wehner, a senior staff scientist at the Lawrence Berkeley National Laboratory, who says it perfectly. "It's not: climate change flooded my house," he explained. "It's: climate change changed the chances of flooding my house."